iommu/ipmmu-vmsa: fix device leak on of_xlate()

iommu/ipmmu-vmsa: fix device leak on of_xlate()

commit 80aa518452c4aceb9459f9a8e3184db657d1b441 upstream.

Make sure to drop the reference taken to the iommu platform device when
looking up its driver data during of_xlate().

Fixes: 7b2d59611fef ("iommu/ipmmu-vmsa: Replace local utlb code with fwspec ids")
Cc: stable@vger.kernel.org	# 4.14
Cc: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>